As stated in your contract, the delivery fee is inclusive of any tax and contribution charges. Therefore, if you intend to include the 4% recalculation in your invoice, the total agreed and paid amount will remain unchanged.
If you want to include the 4% in the invoice, we kindly ask you to opt out from Self Billing, so you can issue your own invoices. If you want to issue your own invoices, please contact us via the Help section of the Rider website.